A rotating electric machine in which permanent magnets are used in a rotor rotates the rotor by interaction between a magnetic field generated by each permanent magnet embedded in the rotor and a magnetic field generated by applying a current to a coil provided in a stator, thereby providing power. Such a rotating electric machine has been widely used in an electric compressor of a refrigeration/air-conditioning apparatus such as an air-conditioning apparatus or a freezer using a refrigeration cycle, a motor generator of an electric vehicle or a hybrid electric vehicle, and the like.
The rotor of such a rotating electric machine is configured by stacking a plurality of core plates, each composed of a circular electromagnetic steel sheet having a plurality of magnet insertion holes, such that n-fold symmetry is achieved so as to correspond to a number of magnetic poles n (n is an even number equal to or greater than 2). In each core plate, a region forming the center side with respect to the magnet insertion holes forms an inner peripheral side core portion, and a region forming the outer peripheral side with respect to the magnet insertion holes forms an outer peripheral side core portion. The inner peripheral side core portion and the outer peripheral side core portion are connected to each other via a plurality of connection portions.
In the rotor of the rotating electric machine configured as described above, a part of a magnetic flux generated from the permanent magnet embedded in each magnet insertion hole does not reach the stator, and a magnetic short circuit occurs in which a loop is formed so as to pass through the inner peripheral side core portion, the connection portions, and the outer peripheral side core portion and be closed at the front and the back of the permanent magnet. Since the magnetic flux due to the magnetic short circuit does not reach the stator, the magnetic flux does not contribute to rotation of the rotor at all and becomes a leakage magnetic flux. Thus, such a magnetic flux becomes a factor for decreasing the performance of the rotating electric machine. In order to reduce such a magnetic short circuit, it is effective to decrease the cross-sectional area of each connection portion thereby to increase the magnetic resistance of each connection portion. The cross-sectional area of each connection portion can be decreased by decreasing the width of the connection portion or decreasing the thickness of the connection portion.
For example, in the rotor of a conventional rotating electric machine, a recess portion is formed in each connection portion, with a width equal to ⅓ to ½ of the width of the connection portion, by thinning a portion of the connection portion close to a magnet insertion hole by means of coining performed by pressing, whereby the cross-sectional area of the connection portion is decreased (see, for example, Patent Document 1).